Tvheadend

h1. Home Tv Streaming Protocol (HTSP) - Version 6

h2. General

HTSP is a TCP based protocol primarily intended for streaming of live TV and related meta data such as channels, group of channels (called tags in HTSP) and electronic program guide (EPG) information.

The transmission and reception of a channel over HTSP is referred to as a subscription. A single HTSP session can handle as many concurrent subscriptions as the bandwidth and CPU permits.

The HTSP server in tvheadend has a payload-aware scheduler for prioritizing more important packets (such as I-frames) before less important ones (such as B-frames). This makes HTSP suitable for long-distance transmissions and/or paths with non-perfect delivery.
(It has been tested with a server in Stockholm and the client in Berlin).

For information about the HTSP wire format please read [[htsmsgbinary|HTSMSG binary format]]

If you're looking to develop a new client, there are several existing client implementations from which you might be able to gain knowledge:

* "XBMC":https://github.com/opdenkamp/xbmc/tree/master/xbmc/pvrclients/tvheadend
* "Showtime":https://github.com/andoma/showtime/tree/master/src/backend/htsp
* "TVHGuide":https://github.com/john-tornblom/TVHGuide
* "PyHTSP":https://github.com/adamsutton/tvheadend/tree/master/support/htsp.py (This is a demo client and is WIP, it has limited functionality).

----

h2. Communication

This communication is currently implemented by using htsmsg:s. All strings are encoded as UTF-8.

There are two distinct ways for communication within HTSP.

Apart from this there is a number of messages that needs to be exchanged during login, see the login section below.

h3. RPC communication

There is a normal RPC way of doing things. I.e. the client sends a request and the server responds with a reply. All the RPC methods are listed below as the 'Client to Server' methods. Apart from all message fields listed within each message type the client can add an additional field:

RPC request extra fields:
<pre>
seq int optional Sequence number. This field will be echoed back by the server in the reply.
username str optional Username, in combination with 'digest' this can be used to raise the privileges
for the session in combination with invocation of a method.
digest bin optional Used to raise privileges.
</pre>

The followings field should be used by the client to match the reply with the request.
All replies are guaranteed to arrive in the same order as the requests.
Even so, probably the best way to implement the request-reply client is by taking advantage of the 'seq' field.

RPC reply extra fields:
<pre>
seq int optional Sequence number. Same as in the request.
error str optional If present an error has occurred and the text describes the error.
noaccess int optional If present and set to '1' the user is prohibited from invoking the method due to
access restrictions.
</pre>

h3. Streaming communication

For streaming of live TV and various related messages the server will continuously push data to the client.
These messages are referred to as asynchronous messages and always have the 'method' field set and never have the 'seq' field set.
Also, the client can enable an additional asyncMetadata mode and by doing so it will be notified by the server when meta data changes. (EPG updates, creation of channels and tags, etc).

h3. Authentication

In Tvheadend, each method has an associated access restriction. Currently there is only one restriction (Streaming). However, this may change in the future.

Privileges for these restrictions may be granted in two ways: Username + Password and/or Source IP address.
Therefore it is possible to gain permissions to the system without entering a username and password.
While this is really useful it also complicates the authentication schema a bit.
Upon connect the initial privileges will be raised based on the source address.

Before any username / password based authentication has taken place the client must have
obtained a challenge (which stays fixed for the session). This is done via the 'hello' method.

In principle it's possible to use two different authentication idioms with HTSP.
Depending on how your application works one or another may be more suitable.
While they do not really differ from a protocol point of view it's worth mentioning a bit about them here:

h3. Initial login authentication

The client performs all of its authentication using the 'login' method.

It may choose to send:
* Username and password: Privileges will be raised based on these credentials.
* Username only: Privileges will be based on just the source address. The username will be used for various logging purposes.
* Nothing: Privileges will be based on just the source address.

If no privileges are granted after the login message has been received by the server (i.e. both network and username + password based)
the server will reply with 'noaccess' set to 1. A client that only employs initial login should honor this flag and ask the
user for a username + password and retry by using the 'authenticate' method. I.e. it should not send the 'login' method again.

h3. On-demand authentication

The client performs all of its authentication when it needs to.

When using this method, the client will check every RPC reply for the 'noaccess' field.
If it set to 1 it whould ask the user for username + password and retry the request but also
add 'username' and 'digest' to the original message. (See _RPC request extra fields_ above)

Typically it would not send a username or digest during login.

----

h2. Client to Server (RPC) methods

h3. hello

Used to identify the client toward the server and to get the session challenge used to
hash passwords into digests. The client can request a different version of the HTSP
protocol with this method. If no 'hello' message is sent the server assumes latest version
is to be used.

Client/Server should select lowest common version, if this is not possible connection should be terminated.

Request message fields:
<pre>
htspversion u32 required Client preferred HTSP version.
clientname str required Client software name.
clientversion str required Client software version.
</pre>

Reply message fields:
<pre>
htspversion u32 required The server supports all versions of the protocol up to and including this number.
servername str required Server software name.
serverversion str required Server software version.
servercapability str[] required Server capabilities (Added in version 6)
challenge bin required 32 bytes randomized data used to generate authentication digests
</pre>

h3. authenticate

This can be used to issue authentication without doing anything else.
If no privileges are gained it will return with 'noaccess' set to 1.

Request message fields:
<pre>
None
</pre>

Reply message fields:
<pre>
noaccess u32 optional If set to 1, no privileges were granted.
</pre>

----

h3. getDiskSpace (Added in version 3)

Return diskspace status from Tvheadend's PVR storage

Request message fields:
<pre>
None
</pre>

Reply message fields:
<pre>
freediskspace s64 required Bytes available.
totaldiskspace s64 required Total capacity.
</pre>

h3. getSysTime (Added in version 3)

Return system time on the server.

Request message fields:
<pre>
None
</pre>

Reply message fields:
<pre>
time s64 required UNIX time.
timezone s32 required Minutes west of GMT.
</pre>

----

h3. enableAsyncMetadata

When this is enabled the client will get continuous updates from the server about added, update or deleted channels, tags, dvr and epg entries.

An interactive application that presents the user with information about these things should probably enable this and the implement the various server to client methods.

Request message fields:
<pre>
epg u32 optional Set to 1, to include EPG data in async, implied by epgMaxTime (Added in version 6).
lastUpdate s64 optional Only provide metadata that has changed since this time (Added in version 6).
epgMaxTime s64 optional Maximum time to return EPG data up to (Added in version 6)
language str optional RFC 2616 compatible language list (Added in version 6)
</pre>

Reply message fields:
<pre>
None
</pre>

Once the reply as been sent the initial data set will be provided, and then updates will arrive asynchronously after that. The initial data dump is sent using the following messages:

<pre>
tagAdd optional
channelAdd optional
tagUpdate optional
dvrEntryAdd optional
eventAdd optional (Added in version 6)
initialSyncComplete required
</pre>

----

h3. getEvent

Request information about the given event. An event typically corresponds to a program on a channel.

The language field in the request allows preference for languages to be requested for the various string fields.

Request message fields:
<pre>
eventId u32 required Event ID.
language str optional RFC 2616 compatible language list (Added in version 6)
</pre>

Reply message fields:
<pre>
see eventAdd
</pre>

h3. getEvents (Added in version 4)

Request information about a set of events. If no options are specified the entire EPG database will be returned.

Request message fields:
<pre>
eventId u32 optional Event ID to begin from (Optional since version 6)
channelId u32 optional Channel ID to get data for (Added in version 6)
numFollowing u32 optional Number of events to add (Optional since version 6)
maxTime u64 optional Maximum time to return data up to (Added in version 6)
language str optional RFC 2616 compatible language list (Added in version 6)
</pre>

Reply message fields:
<pre>
events msg[] required List of events, using response message fields from eventAdd
</pre>

h3. epgQuery (Added in version 4)

Query the EPG (event titles) and optionally restrict to channel/tag/content type.

Request message fields:
<pre>
query str required Title regular expression to search for
channelId u32 optional [[ChannelId]] to restrict search to
tagId u32 optional [[TagId]] to restrict search to
contentType u32 optional DVB content type to restrict search to
language str optional RFC 2616 compatible language list for title (Added in version 6)
full u32 optional Output full event list rather than just IDs
</pre>

Reply message fields:

if full == 1
<pre>
events msg[] optional List of events, using response message fields from eventAdd
</pre>
else
<pre>
eventIds u32[] optional List of eventIds that match the query
</pre>

h3. getEpgObject

Get detailed EPG Object info.

Request message fields:
<pre>
id u32 required Object ID
type u32 optional Object type
</pre>

Reply message fields:

<pre>
TODO
</pre>

----

h3. addDvrEntry (Added in version 4)

Create a new DVR entry. Either eventId or channelId, start and stop must be specified.

Request message fields:
<pre>
eventId u32 optional Event ID (Optional since version 5).
channelId u32 optional Channel ID (Added in version 5)
start s64 optional Time to start recording (Added in version 5)
stop s64 optional Time to stop recording (Added in version 5)
creator str optional Name of the event creator (Added in version 5)
priority u32 optional Recording priority (Added in version 5)
startExtra s64 optional Pre-recording buffer in minutes (Added in version 5)
stopExtra s64 optional Post-recording buffer in minutes (Added in version 5)
title str optional Recording title, if no eventId (Added in version 6)
description str optional Recording description, if no eventId (Added in version 5)
configName str optional DVR configuration name
</pre>

Reply message fields:
<pre>
success u32 required 1 if entry was added, 0 otherwise
id u32 optional ID of created DVR entry
error str optional English clear text of error message
</pre>

h3. updateDvrEntry (Added in version 5)

Update an existing DVR entry.

Request message fields:
<pre>
id u32 required DVR Entry ID
start s64 optional New start time
stop s64 optional New stop time
title str optional New entry title
description str optional New entry description (Added in version 6)
startExtra s64 optional New pre-record buffer (Added in version 6)
stopExtra s64 optional New post-record buffer (Added in version 6)
configName str optional New DVR configuration name
</pre>

Reply message fields:
<pre>
success u32 required 1 if update as successful, otherwise 0
error str optional Error message if update failed
</pre>

h3. cancelDvrEntry (Added in version 5)

Cancel an existing recording, but don't remove the entry from the database.

Request message fields:
<pre>
id u32 required dvrEnryId to delete
</pre>

Reply message fields:
<pre>
success int required 1 if entry was cancelled
error str optional Error message if cancellation failed
</pre>

h3. deleteDvrEntry (Added in version 4)

Delete an existing DVR entry from the database.

Request message fields:
<pre>
id u32 required DVR Entry ID
</pre>

Reply message fields:
<pre>
success u32 required 1 if entry was removed
error str optional Error message if the delete fails
</pre>

----

h3. getTicket (Added in version 5)

Get a ticket to allow access to a channel or recording via HTTP

Request message fields:
<pre>
channelId u32 optional Channel to gain access for
dvrId u32 optional DVR file to gain access for
</pre>

Reply message fields:
<pre>
path str required The full path for access URL (no scheme, host or port)
ticket str required The ticket to pass in the URL query string
</pre>

h3. subscribe

Request subscription to the given channel.

Request message fields:
<pre>
channelId u32 required ID for channel.
subscriptionId u32 required Subscription ID. Selected by client. This value is not interpreted by the server in any form.
The value is used from now on in all messages related to the subscription.
weight u32 optional Weighting of this subscription (same as recording priority).
</pre>

Reply message fields:
<pre>
None
</pre>

h3. unsubscribe

Stop a subscription.

Request message fields:
<pre>
subscriptionId u32 required Subscription ID.
</pre>

Reply message fields:
<pre>
None
</pre>

h3. subscriptionChangeWeight (Added in version 5)

Change the weight of an existing subscription

Request message fields:
<pre>
subscriptionId u32 required Subscription ID.
weight u32 optional The new subscription weight.
</pre>

Reply message fields:
<pre>
None
</pre>

h1. Server to Client methods

----

h3. channelAdd

A new channel has been created on the server.

Message fields:
<pre>
channelId u32 required ID of channel.
channelNumber u32 required Channel number, 0 means unconfigured.
channelName str required Name of channel.
channelIcon str optional URL to an icon representative for the channel.
eventId u32 optional ID of the current event on this channel.
nextEventId u32 optional ID of the next event on the channel.
tags u32[] optional Tags this channel is mapped to.
services msg[] optional List of available services (Added in version 5)
</pre>

Service fields:
<pre>
name str required Service name
type str required Service type
caid u32 optional Encryption CA ID
caname str optional Encryption CA name
</pre>

h3. channelUpdate

Same as channelAdd, but all fields (except channelId) are optional.

h3. channelDelete

A channel has been deleted on the server.

Message fields:
<pre>
channelId u32 required ID of channel.
</pre>

----

h3. tagAdd

A new tag has been created on the server.

Message fields:
<pre>
tagId u32 required ID of tag.
tagName str required Name of tag.
tagIcon str optional URL to an icon representative for the channel.
tagTitledIcon u32 optional Icon includes a title
members u32[] optional Channel IDs of those that belong to the tag
</pre>

h3. tagUpdate

Same as tagAdd, but all fields (except tagId) are optional.

h3. tagDelete

A tag has been deleted from the server.

Message fields:
<pre>
tagId u32 required ID of tag.
</pre>

----

h3. dvrEntryAdd (Added in version 4)

A new recording has been created on the server.

Message fields:
<pre>
id u32 required ID of dvrEntry.
channel u32 required Channel of dvrEntry.
start s64 required Time of when this entry was scheduled to start recording.
stop s64 required Time of when this entry was scheduled to stop recording.
eventId u32 optional Associated EPG Event ID.
title str optional Title of recording
summary str optional Short description of the recording (Added in version 6).
description str optional Long description of the recording.
state str required Recording state
error str optional Plain english error description (e.g. "Aborted by user").
</pre>

TODO: recording states

h3. dvrEntryUpdate

Message fields:
<pre>
Same as dvrEntryAdd, but all fields (except id) are optional.
</pre>

h3. dvrEntryDelete (Added in version 4)

A recording has been deleted from the server.

Message fields:
<pre>
id u32 required ID of recording to delete.
</pre>

----

h3. eventAdd (Added in version 6)

Message fields:
<pre>
eventId u32 required Event ID
channelId u32 required The channel this event is related to.
start u64 required Start time of event, UNIX time.
stop u64 required Ending time of event, UNIX time.
title str optional Title of event.
summary str optional Short description of the event (Added in version 6).
description str optional Long description of the event.
serieslinkId u32 optional Series Link ID (Added in version 6).
episodeId u32 optional Episode ID (Added in version 6).
seasonId u32 optional Season ID (Added in version 6).
brandId u32 optional Brand ID (Added in version 6).
contentType u32 optional DVB content code (Added in version 4, Modified in version 6*).
ageRating u32 optional Minimum age rating (Added in version 6).
starRating u32 optional Star rating (1-5) (Added in version 6).
firstAired s64 optional Original broadcast time, UNIX time (Added in version 6).
seasonNumber u32 optional Season number (Added in version 6).
seasonCount u32 optional Show season count (Added in version 6).
episodeNumber u32 optional Episode number (Added in version 6).
episodeCount u32 optional Season episode count (Added in version 6).
partNumber u32 optional Multi-part episode part number (Added in version 6).
partCount u32 optional Multi-part episode part count (Added in version 6).
episodeOnscreen str optional Textual representation of episode number (Added in version 6).
image str optional URL to a still capture from the episode (Added in version 6).
dvrId u32 optional ID of a recording (Added in version 5).
nextEventId u32 optional ID of next event on the same channel.
</pre>

* *contentType previously had the major DVB category in the bottom 4 bits,
however in v6 this has been changed to properly match DVB, so top 4 bits
as major category and bottom 4 bits has sub-category. Clients requesting
v5 or lower will get the old output.

h3. eventUpdate (Added in version 6)

Message fields:
<pre>
Same as eventAdd but all fields (except eventId) are optional.
</pre>

h3. eventDeleted (Added in version 6)

Message fields:
<pre>
eventId u32 required Event ID
</pre>

---

h3. initialSyncCompleted (Added in version 2)

Sent after all the initial metadata has been sent when session has been set to async mode.

Message fields:
<pre>
</pre>

----

h3. subscriptionStart

Asynchronous message output when a new subscription is successfully started.

Message fields:
<pre>
subscriptionId u32 required Subscription ID.
streams msg[] required Array of messages with stream information
sourceinfo msg optional Source information.
</pre>

Stream message fields:
<pre>
index u32 required Index for this stream
type str required Type of stream
language str optional Language for stream
Video components only:
width u32 optional Width of video in pixels
height u32 optional Height of video in pixels
aspect_num u32 optional Aspect ratio numerator (Added in version 5)
aspect_den u32 optional Aspect ratio denonminator (Added in version 5)
Audio components only:
channels u32 optional Number of audio channels (Added in version 5)
rate u32 optional Audio bitrate (Added in version 5)
Subtitle components only:
composition_id u32 optional ??? (Added in version 5)
ancillary_id u32 optional ??? (Added in version 5)
</pre>

Sourceinfo message fields:
<pre>
adapter str optional Adapter name
mux str optional Transponder name
network str optional Network name
provider str optional ???
service str optional Service name
</pre>

Video Stream types:
<pre>
MPEG2VIDEO MPEG2 video
H264 H264 video
</pre>

Audio Stream types:
<pre>
MPEG2AUDIO MPEG2 audio (MP2)
AC3 AC3 audio
AAC ADTS framed AAC (one AAC packet per ADTS frame)
EAC3 Enhanced AC3 audio
</pre>

Subtitle Stream types:
<pre>
TELETEXT ???
DVBSUB ???
</pre>

h3. subscriptionStop

A subscription has been stopped.

Message fields:
<pre>
subscriptionId u32 required Subscription ID.
status str optional Error message if subscription stopped unexpectedly.
</pre>

h3. subscriptionStatus

Subscription status update.

Message fields:
<pre>
subscriptionId u32 required Subscription ID.
status str optional English clear text of error status. Absence of this field means that the status is OK.
</pre>

h3. queueStatus

The queueStatus message is sent every second during normal data delivery.

The transmit scheduler have different drop thresholds for different frame types.

If congestion occurs it will favor dropping B-frames before P-frames before I-frames.
All audio is recognized as I-frames.

Message fields:
<pre>
subscriptionId u32 required Subscription ID.
packets u32 required Number of data packets in queue.
bytes u32 required Number of bytes in queue.
delay u32 optional Estimated delay of queue (in µs).
Bdrops u32 required Number of B-frames dropped
Pdrops u32 required Number of P-frames dropped
Idrops u32 required Number of I-frames dropped
</pre>

h3. signalStatus

The signalStatus message is sent every second during normal data delivery.

The optional fields may not have been implemented or may not be supported by the active adapter.

Message fields:
<pre>
subscriptionId u32 required Subscription ID.
feStatus str required Frontend status.
feSNR u32 optional Signal to noise ratio.
feSignal u32 optional Signal status percentage.
feBER u32 optional Bit error rate.
feUNC u32 optional Uncorrected blocks.
</pre>

h3. muxpkt

Streaming data.

Message fields:
<pre>
subscriptionId u32 required Subscription ID.
frametype u32 required Type of frame as ASCII value: 'I', 'P', 'B'
stream u32 required Stream index. Corresponds to the streams reported in the subscriptionStart message.
dts s64 optional Decode Time Stamp in µs.
pts s64 optional Presentation Time Stamp in µs.
duration u32 required Duration of frame in µs.
payload bin required Actual frame data.
</pre>